Understanding xDNA match when no atDNA?

Question

What does it mean when I have no shared atDNA but a small amount of xDNA with a male match?

It's a minute amount of X at 14 but this fellow would like to try & track where we intersect.

I'm just getting my head around the atDNA & have no clue about this one at all.

Hi, welcome to G&FH.SE! Do you mean that your shared segment on the X chromosome is 14 cMs? — Jan Murphy, Oct 25 '18 at 20:40

score 1 · Answer 1 · answered Oct 25 '18 at 18:01

The small amount of shared xDNA means nothing valuable. The reasoning is that xDNA is relatively short when comparing to the whole set of atDNA. The only thing that is specific for xDNA is the inheritance pattern (males have only one X and females have two X). So xDNA in combination with Y-DNA/mtDNA and atDNA MAY give additional clues. But MAY not give.

If you want more precise answer, please give more input information, but I bet that there is no historically/genetically significant relationship (like 8-rd cousins or other) between mentioned two persons.

score 0 · Answer 2 · edited Oct 26 '18 at 20:01

Two ways you can look at this:

For a distant match you might have one or two small segments on any given chromosome(s). And the X is as good as any other for this.
Because the X recombines less often (since males (usually) only have one X), often the segments you see matching on an X will represent a common ancestor further back than they might if on Chrom 1-22. That's by average and doesn't necessarily mean anything for an individual, since there's a wide range of how far back a tiny match can go.

Understanding xDNA match when no atDNA?

2 Answers2